[Focus on preanalytics for Down's syndrome screening during first trimester of pregnancy].

The aim of the study is to specify the pre-analytical conditions required for Down's syndrome screening in first trimester by maternal serum markers. The concentration variation of both markers, hCGβ and PAPP-A, was analyzed at room temperature, at 4°C and during freezing-thawing cycles. Serum can be kept during 72h between 2 and 8°C with an acceptable bias of 5% for each marker. It can also undergo three freezing-thawing cycles without any variation of results. Preservation at room temperature (between 20 and 25°C) requires an analysis within 24h. From this study, writing recommendations enable to give a precise frame to pre-analytical processing and transport of blood samples, in a field where variations can lead to heavy therapeutic decisions.